Manufacture of benzene hexachloride



April 12, 1955 J. H. DUNN ETAL MANUFACTURE OF BENZENE HEXACHLORIDE FiledSept. 23. 1952 khkms SSQQ LEM K vw

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JAMES H. DUNN STB'HEN III. HALL LEO A. MILLER CLARENCE Al. NEWERATTORNEY United States Patent OfiFice 2,706,172 Patented Apr. 12, 1955MANUFACTURE OF BENZENE HEXACHLORIDE James H. Dunn, Stephen N. Hall, LeoA. Miller, and Clarence M. Neher, Baton Rouge, La., assignors to EthylCorporation, New York, N. Y., a corporation of Delaware ApplicationSeptember 23, 1952, Serial No. 311,034

2 Claims. (Cl. 204-163) This invention relates to the manufacture ofbenzene hexachloride and more particularly to the recovery ofbenzene-free benzene hexachloride from reactor solution.

This application is a continuation-in-part of our copending application,Serial No. 92,268, filed May 10, 1949, now Patent 2,622,105.

In the manufacture of benzene hexachloride (BHC), benzene is reactedwith chlorine in the presence of actinic light using excess quantitiesof benzene. The product is generally obtained as a 15 to 25 per centsolution of BHC in benzene. One method for the recovery of the benzenehexachloride product from the benzene solvent comprises scrubbing thereacted solution to remove unreacted chlorine, separating theBHC-containing benzene from the immiscible aqueous caustic phase,evaporating the benzene, and recovering the benzene hexachloride.

The above means of BHC recovery produces a high quality, white product,and provides numerous other advantages over steam distillation andsimilar recovery techniques, heretofore employed. However, the causticscrubbing technique, discussed above, has a number of inherentdisadvantages which reduce its value in large scale commercialoperation. These disadvantages are as follows:

The valuable chlorine, dissolved in the reaction prodnet, is degradedwhen neutralized with caustic soda, resulting in the formation oflow-value sodium chloride;

The cost of the caustic soda, used for neutralization, is a large partof the total cost of the BHC manufacturing process;

The caustic scrubbing operation requires expensive processing equipment;

The vaporization of all of the benzene in a single step requiresexcessive quantities of high pressure steam.

Sodium chloride and other corrosion elements, which are dissolved in thereactor solution following caustic scrubbing, present serious corrosionproblems in the final benzene vaporization operation.

It is accordingly an object of the present invention to provide animproved process for the recovery of benzene hexachloride from benzenesolutions containing the same. Another object is to provide a process ofthe above type in which unreacted chlorine normally dissolvedin thechlorination reaction product can be recovered as free chlorine. Anotherobject is to provide an economical process of the above type whicheliminates the need for a caustic wash, permits the use of low pressuresteam, and reduces or eliminates corrosive materials in the reactorsolution prior to vaporization of the benzene.

The present invention accomplishes all of the above objects by effectingvaporization of the benzene in a plurality of stages. Upon chlorinationof benzene in a suitable reactor, the benzene reactor solution(containing benzene, BHC, chlorine, hydrogen chloride, and sometimeswater) is passed into a first vaporizer wherein sufiicient benzene isvaporized to remove the major quantities of dissolved chlorine andhydrogen chloride. This vaporization is preferably controlled to producean essentially saturated solution of benzene hexachloride in benzene atthe temperature of vaporization. It is not desired to remove in thisstep a suflicient quantity of benzene to precipitate appreciablequantities of BHC in the concentrated reactor solution. Theso-concentrated solution is then passed into a second vaporizer whereinthe remaining quantities of the benzene are vaporized.

The benzene reactor solution is normally essentially saturated withbenzene hexachloride under the conditions of thereaction, i. e., 10-25per cent by weight BHC in benzene. This reactor solution is then passedinto the vaporizer or concentrator wherein the temperature of thereactor solution (generally above about F.) is raised to a temperaturebetween and 225 F. (76- 107 C.), preferably between 170 and F. (76- 88C.). These temperatures can be somewhat lower if reduced pressures areemployed. The solution in this operation is concentrated, for example,from approximately a 15 per cent by weight BHC solution to between a 30to 50 per cent by weight BHC solution, preferably about 40 per cent byweight.

The reactor solution normally contains from 0.25 to 3 per cent chlorine,less than 1 per cent HCl, and about 1 per cent of water. These volatileimpurities are removed from the reactor solution during the lattervaporization or concentration operation, and these vapors can then berecovered by any suitable recovery equipment. However, a very desirablemethod is disclosed hereinafter for selectively dissolving the valuablechlorine from the hydrogen chloride gas.

The concentrated benzene solution is then passed into a second vaporizeroperated at a temperature between 320420 F. (1602l5 C.) and preferablybetween 350-370 F. (l76188 C.) wherein the remaining benzene is flashedfrom the BHC. The solvent-free BHC, in a molten condition at thesetemperatures, is then solidified and recovered. The latter recovery ofthe BHC can conveniently be accomplished by use of a drum flaker orsimilar apparatus.

A wide variety of process equipment can be employed for either theconcentration operation or the final flash vaporization operation. Forexample, either unit can be simply a conventional heat exchanger incombination with a knockout drum or similar vessel. Details of a highlydesirable process and apparatus for the final vapor-izer is disclosed inU. S. Patent No. 2,564,406.

For a better understanding of the operation of the invention, onemodification of a suitable process flow diagram and apparatus isillustrated in the drawing. The main units of equipment for the benzenevaporization operation are the concentrator 10, a concentrator knockoutdrum 20, a flash vaporizer 30, including a knockout drum 32 and a drumflaker or caster 40. The main vapor recovery units are a concentratorcondenser 50, a benzene feed drum 60, a vent scrubber 70 and a vaporizercondenser 80.

A benzene-BHC reactor solution, obtained by any suitable process, ispassed into the bottom of the concentrator 10, through the line 12. Theconcentrator, as shown, is a tube bundle heat exchanger. The benzenesolution flows upwardly through the plurality of tubes 14. Steam orother heat transfer medium enters the jacket of the concentrator 10through line 16 and leaves through the line 18. The mixture of vaporsand concentrated BHC solution is then passed through line 22 into theconcentrator knockout drum 2%) where the phases are separated. Theconcentrated BHC solution 24 then flows to the flash vaporizer 30,through the line 34, wherein the remaining benzene is flashed. Thisvaporizer is also shown as a tube bundle heat exchanger in which the BHCsolution flows through a plurality of tubes (not shown). A heat transfermedium, preferably high pressure steam, enters the jacket of the flashvaporizer through the line 36 and leaves the same through the line 38.Molten BHC separates from the benzene vapors in the vaporizer knockoutdrum 32 and is solidified and flaked by the drum caster 40. In thelatter operation, molten BHC in the pan 42 freezes on the cooled rollerand is flaked off therefrom by a knife or similar scraper.

The vapors formed in the concentrator 10 and separated from the liquidphase in the knockout drum 20 are passed to the concentrator condenser50, through the line 52. This condenser is shown in the: drawing as atube bundle heat exchanger, and is cooled by any suitable coolingmedium, flowing through the lines 54 and 56. Condensed vapors, primarilybenzene, are returned to the benzene feed drum 60, through the line 62.The uncondensed vapors are passed from the concentrator condenser 50 tothe vent scrubber 70, through the line 72, wherein the vapors arescrubbed essentially free of chlorine with fresh benzene. The freshbenzene enters the vent scrubber through the line 74 from the benzenefeed drum 60. The'benzene solution containing the unreacted chlorine isreturned to the benzene feed drum 60 through the line 64. The so-crubbedgases, primarily hydrogen chloride, are then recovered or disposed of byany suitable means.

The benzene vaporized in the flash vaporizer and separated from themolten BHC in the knockout drum 32 is passed into the vaporizercondenser through line 82. The condensed benzene vapors are returnedthrough line 66 to the benzene feed drum.

The following is a working example of a commercial scale recoveryoperation. A benzene reactor solution containing 17 weight per cent BHCis fed to the concentrator 10 through the line 12, at a rate of 23,590parts by weight/hour. The solution also contains about 3 per cent byweight of chlorine and traces of water and HCl at 2" of water pressure.This reactor solution has a temperature of F.

In the concentrator 10, the temperature of the solution is raised to 187F. The mixture of concentrated solution and vapor formed therein is thenseparated in the BHC concentrator knockout drum 20. The concentratedfeed, 40 per cent by weight BHC in benzene, is passed to the flashvaporizer 30 through the line 34 at the rate of 9,200 parts byweight/hour and is essentially free of chlorine, HCl or water. In theflash vaporizer 30, the temperature of the solution is raised to about360 F. At this temperature, the benzene and molten BHC are separated inthe knockout drum 32, and the BHC is recovered as a white, flaky productfrom the drum caster 40 at the rate of 3,425 parts by weight/ hour. Thevaluable unreacted chlorine, about parts by weight/hour, is recovered inthe vent scrubber 70. The vapor phase from the concentrator knockoutdrum 20 is fed at the rate of 14,440 parts by weight/hour to theconcentrator condenser wherein essentially all benzene is condensed andreturned through the line 62 to the benzene feed drum 60. Thetemperature of this condensation is 176 F. The un condensed phasecontaining the chlorine is then passed through the line 72 to the ventscrubber wherein cool 100 F.) benzene from the benzene feed drum 60 isused to scrub the vapors. This benzene passes through the line 74. Thebenzene containing the chlorine is then returned to the benzene feeddrum through the line 64.

As is believed apparent from the foregoing, the present inventionprovides an improved process for the economi-.

cal recovery of BHC from solutions thereof in benzene whereby a white,flaky BHC product can be obtained. This process, in contrast to priorprocesses, permits the recovery of unreacted gaseous chlorine from a BHCreactor Solution, eliminates corrosive conditions during the final flashvaporization of benzene from the BHC and permits the use of lowtemperature steam for vaporization of large quantities of the benzenesolvent.

We claim:

1. A process for the manufacture of crude benzene hexachloridecomprising chlorinating benzene in the presence of actinic light toproduce a product containing benzene hexachloride, hydrogen chloride andunreacted chlorine dissolved in benzene, thereafter vaporizing a firstpot tion of the benzene, the hydrogen chloride and the unreactedchlorine at a temperature between about to 225 F. to concentrate thebenzene hexachloride in ben zene solution, heating the so-concentratedsolution to a temperature between about 350370 F. to remove theremaining benzene and recover the crude benzene hexachloride, coolingthe vapors containing the first portion of benzene, the hydrogenchloride and chlorine to condense and separate the benzene from theunreacted chlo rine and hydrogen chloride, scrubbing the uncondensedvapors with cool benzene to selectivelydissolve the unreacted chlorinefrom the hydrogen chloride, and recycling the benzene used in thescrubbing operation and containing the unreacted chlorine for furtherchlorina- Hon.

2. A process for the manufacture of crude benzene hexachloridecomprising chlorinating benzene in the presence of actinic light toproduce a product containing benzene hexachloride, hydrogen chloride andunreacted chlorine dissolved in benzene, thereafter vaporizing a firstportion of the benzene, the hydrogen chloride and the unreacted chlorineat a sulficiently high temperature to concentrate the benzenehexachloride in benzene solution, heating the so-concentrated solutionto a substantially higher temperature sufficient to remove the remainingbenzene and recover the crude benzene hexachloride, cooling the vaporscontaining the first portion of benzene, the hydrogen chloride andchlorine to condense and separate the benzene from the unreactedchlorine and hydrogen chloride, scrubbing the uncondensed vaporswithscool benzene to selectively dissolve the unreacted chlorine fromthe hydrogen chloride, and recycling the benzene used in the scrubbingoperation and containing the unreacted chlorine for furtherchlorination.

References Cited in the file of this patent UNITED STATES PATENTS2,628,260 Britton et a1. Feb. 10, 1953 FOREIGN PATENTS 646,917 GreatBritain Nov. 29, 1950 655,686 Great Britain Aug. 1, 1951

1. A PROCESS FOR THE MANUFACTURE OF CRUDE BENZENE HEXACHLORIDECOMPRISING CHLORINATING BENZENE IN THE PRESENCE OF ACTINIC LIGHT TOPRODUCE A PRODUCT CONTAINING BENZENE HEXACHLORIDE, HYDROGEN CHLORIDE ANDUNREACTED CHLORINE DISSOLVED IN BENZENE, THEREAFTER VAPORIZING A FIRSTPORTION OF THE BENZENE, THE HYDROGEN CHLORIDE AND THE UNREACTED CHLORINEAT A TEMPERATURE BETWEEN ABOUT 170* TO 225* F. TO CONCENTRATE THEBENZENE HEXACHLORIDE IN BENZENE SOLUTION, HEATING THE SO-CONCENTRATEDSOLUTION TO A TEMPERATURE BETWEEN ABOUT 350* -370* F. TO REMOVE THEREMAINING BENZENE AND RECOVER THE CRUDE BENZENE HEXACHLORIDE, COOLINGTHE VAPORS CONTAINING THE FIRST PORTION OF BENZENE, THE HYDROGENCHLORIDE AND CHLORINE TO CONDENSE AND SEPARATE THE BENZENE FROM THEUNREACTED CHLORINE AND HYDROGEN CHLORIDE, SCRUBBING THE UNCONDENSEDVAPORS WITH COOL BENZENE TO SELECTIVELY DISSOLVE THE UNREACTED CHLORINEFROM THE HYDROGEN CHLORIDE, AND RECYCLING THE BENZENE USED IN THESCRUBBING OPERATION AND CONTAINING THE UNREACTED CHLORINE FOR FURTHERCHLORINATION.